Saltmarsh Mosquito eradicated from Mahia

Saltmarsh Mosquito eradicated from Mahia -- another year for
Hawkes Bay and Gisborne

Health authorities have won a
second battle against the Southern Saltmarsh Mosquito but
warn that the war against the Aussie invader is still far
from over, Associate Biosecurity Minister Marian Hobbs said
today.

No adults or larvae of the saltmarsh mosquito have
been detected in the Mahia Peninsula for two years and the
mosquito is now officially regarded as eradicated from the
area. The mosquito has also been cleared successfully from
Napier where the Australian pest was first detected in 1988.

However eradication continues in nearby Porongahau, the
last remaining Hawkes Bay site where the mosquito has been
detected. It is on target to be cleared in August next year.
Tairawhiti is expected to be cleared a month after that.

Meanwhile the largest eradication programme in the
country is continuing in the Kaipara region, targeting a
potential habitat of 2700 hectares.

The southern
saltmarsh mosquito can carry the Ross River Virus with a
wide range of debilitating symptoms lasting for up to a
month or, in some cases, much longer.

There has never
been a case of the disease contracted in New Zealand and
Marian Hobbs said health and biosecurity authorities want to
keep it that way.

Treatment with an insect growth
regulator S-methoprene and a biological control agent, Bti,
is conducted over the mosquito-breeding season in
summer.

"I'd like to thank everyone involved for their
input. The support for this programme has been really
pleasing, with the community well behind the project,"
Marian Hobbs said.

The southern saltmarsh mosquito is a
particularly aggressive daytime biting mosquito. Mosquitoes
are most active around dawn, late afternoon and just after
dusk. Screening open doors and windows, using insect sprays
or mosquito coils indoors and wearing long clothing and
repellent when outdoors, can reduce the possibility of being
bitten.

Questions and Answers:

What is Ross
River virus? Ross River virus disease is known as epidemic
polyarthritis (inflammation of the joints). Symptoms can be
wide ranging, from pain and tenderness in the muscles and
joints to flu-like symptoms of chills and fevers. Most
people fully recover within a month of the onset of
symptoms. No locally acquired cases of Ross River virus
disease have been reported, however, people carrying Ross
River Virus will be in New Zealand regularly (e.g. tourists
or travellers returning from Australian states where Ross
River Virus is endemic). The Ross River Virus can only be
transmitted by mosquitoes; it cannot spread from person to
person.

What is the southern saltmarsh mosquito life
cycle? The mosquito life cycle has four stages: The EGGS
are laid in water. Southern saltmarsh mosquitoes lay their
eggs above the surface of the water and the eggs do not
hatch until there is a king tide or heavy rainfall to wet
them. The LARVAE hatch out and swim in water. The larvae
stage is when the mosquito is easiest to detect and is most
vulnerable to eradication measures. The PUPAE is the
resting stage between LARVAE and ADULT. The pupa is
difficult to detect. The ADULT is the flying, biting and
egg-laying stage of the mosquito's life cycle.

How much
funding did the Government allocate to controlling and
eradicating exotic mosquitoes earlier this year? The total
funding is approximately $30-million nationwide over four
years. The money will be used to continue the eradication
programme for the exotic mosquito in Tairawhiti, Mahia and
Porangahau as well as the Kaipara and Mangawhai areas. The
eradication phase of the programme in Napier has concluded,
with no sign of southern saltmarsh mosquitoes for over two
years.

What chemicals are being used, and are they safe?
S-methoprene is a slow-release insect growth regulator that
stops the mosquito pupae hatching into adults. It is not a
spray and does not drift. Sand granules are coated in the
active ingredient. It may also be used in pelletised form.
S-methoprene is used against mosquitoes throughout the
world. Bti is also being used in eradication programmes in
Kaipara, Hawke’s Bay and Tairawhiti, and has also been
extensively used in control programmes in Australia, Africa,
the United States and Germany. Both chemicals have
undergone a full health impact assessment in New Zealand.
They break down quickly in the environment and are believed
to be environmentally safe for use in New Zealand. Studies
of non-target species where it has been applied in the
Hawke's Bay have shown no impact.

What would happen if
the eradication programme didn't go ahead? If the southern
saltmarsh mosquito got established in the North Island the
chances of an outbreak of the Ross River virus would be
greatly increased. If someone coming into the country with
the virus in their system was bitten and the mosquito then
bit another person, the virus would be spread to the second
person. An estimate done in 2001 put the cost to the
taxpayer of an outbreak in Auckland alone more than $38
million - and that estimate is thought to be conservative.

Where else are the eradication programmes being carried
out?

Napier and Mahia: This programme has been
completed. Surveillance is continuing as part of the public
health service's routine monitoring of high-risk mosquito
habitats.

Porangahau and Tairawhiti: Applications of
mosquito control agents have been completed at all sites.
The last mosquito found in Porangahau was in August 2002. If
no further larvae or adults are detected, eradication will
be completed in September 2004. The last mosquito detected
in Tairawhiti was in September 2002. If no further adults
or larvae were found, eradication would be completed in
October 2004.

Kaipara: The Kaipara eradication
programme is being fully implemented. Permanent sentinel
surveillance sampling sites have been established at 31
locations including Mangawhai and Whitford, and sites are
visited twice weekly and sampled for adults and larvae.
Sites have been selected to represent known positive areas;
intermittently positive areas and known negative sites and
reports include community reports of unusual biting
activity. Only single adults were found in each of August
and September 2003 and no adults were found in October 2003.
Whitford: After finding several adults and larvae in
February 2002, an eradication programme was begun. There
have been no sightings of mosquitoes for some months now,
and if that continues it's expected the treatment phase will
be able to finish around March 2004 and the area will go
into surveillance phase.

Mangawhai: After the initial
discovery at Mangawhai, north of Kaipara in about April
2001, no further larvae or adult salt marsh mosquitoes were
found at that site for some 15 months. Then following a
large water event a single adult was captured. Surveillance
was stepped up and is ongoing with no further finds of
mosquitoes to date.

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